This invention relates generally to transport refrigeration systems for mobile refrigerated cargo systems and, more particularly, to transport refrigeration systems wherein a prime mover, such as diesel engine, directly or indirectly drives the refrigerant compressor of the transport refrigeration system.
Refrigerated trucks and trailers and intermodal containers, collectively mobile refrigeration systems, are commonly used to transport perishable cargo, such as, for example, produce, meat, poultry, fish, dairy products, cut flowers, and other fresh or frozen perishable products, by road, rail, sea or intermodally. In the case of refrigerated trucks, a transport refrigeration system is mounted to the truck, typically behind the truck or on the roof of the truck for maintaining a controlled temperature environment within the cargo box within the truck. In the case of refrigerated trailers, which are typically pulled behind a tractor cab, a transport refrigeration system is mounted to the trailer, typically to the front wall of the trailer for maintaining a controlled temperature environment within the cargo box of the trailer.
Conventionally, transport refrigeration systems used in connection with refrigerated trucks and refrigerated trailers include a transport refrigeration unit having a refrigerant compressor, a condenser with one or more associated condenser fans, an expansion device, and an evaporator with one or more associated evaporator fans, which are connected via appropriate refrigerant lines in a closed refrigerant flow circuit. Air or an air/gas mixture is drawn from the interior volume of the cargo box by means of the evaporator fan(s) associated with the evaporator, passed through the airside of the evaporator in heat exchange relationship with refrigerant whereby the refrigerant absorbs heat from the air, thereby cooling the air. The cooled air is then supplied back to the cargo box.
On commercially available transport refrigeration systems used in connection with refrigerated trucks and refrigerated trailers, the compressor, and typically other components of the transport refrigeration unit, must be powered during transit by an onboard engine. In the case of refrigerated trailers, the engine typically comprises a diesel engine carried on and considered part of the transport refrigeration system. In mechanically driven transport refrigeration systems the compressor is directly driven by the diesel engine, either through a direct mechanical coupling or a belt drive. An all electric transport refrigeration system for refrigerated trailer application is also commercially available through Carrier Corporation, headquartered in Farmington, Conn., USA. In the all electric transport refrigeration system, the engine, again most commonly a diesel engine, carried on and considered part of the transport refrigeration system, drives an onboard AC synchronous generator that generates AC power. The generated AC power is used to power an electric compressor motor for driving the refrigerant compressor of the transport refrigeration unit.
As noted previously, transport refrigeration systems are provided in connection with mobile refrigeration systems for maintaining a controlled temperature environment within the refrigerated cargo space, such as for example the cargo box of the trailer or truck. Although the refrigeration unit is generally operated in a cooling mode to maintain the temperature within the cargo box at a desired temperature for the product stowed in the cargo box, it may be necessary to actually heat the air within the cargo box particularly in cooler climates and for certain products. Generally, it is also necessary to heat the evaporator coil to melt frost from the outside surface of the evaporator coil. Therefore, the refrigeration unit may be designed for operation in a heating mode and a defrost mode wherein hot refrigerant vapor is directed from the compressor discharge directly to and through the evaporator coil to heat box air passed through the evaporator by the evaporator fan. Alternatively, an electric resistance heater may be provided in proximity to the evaporator coils that may be selectively activated to heat the box air passing through the evaporator or to melt frost off the evaporator coil.
Although both of the aforementioned systems perform well in heating the circulating cargo box air and in defrosting the evaporator coil, both systems require operation of the engine to either drive the compressor for circulating hot refrigerant vapor through the evaporator coil or to drive a generator for producing the electric power to operate the resistance heater, which increases the shaft load on the engine during operation of the refrigeration unit in the heating mode.